1. Field of the Invention
The present invention relates to temperature controlled mattress pads, seats or other cushions, and more particularly to such a cushion that is heated by a positive temperature coefficient (PTC) element and ventilated as well.
2. Description of the Related Art
Resistance wires oftentimes with PTC (positive temperature coefficient) resistive elements are the conventional way of heating a cushion by conduction. This suffers from certain disadvantages, however, including that the electrical conductors are located within the cushion itself. Over time, the wires, carbon fiber strips or the like being subject to repeated weight loads and mechanical stresses may become physically damaged causing sparks from short circuits, and an occasional fire. Voltages as low as 6V can produce noticeable sparking, even at current levels in the 1-200 milliamp range.
Insulation is commonly used in the prior art, not only to limit peak heating at the conductor but also to spread the heating effect out (or average it) over the surface to be heated. The disadvantage here is that it takes longer to reach an adequate heating level, because of the drop in heating efficiency caused by the insulation. The overall efficiency of the heating apparatus is compromised as the insulation slows the heating of the outer surface of the cushion.
Other problems with the prior art heated cushions include operator errors in sewing the wire into the cushion leading to warranty claims. When wire mats are used they are generally not air permeable, preventing the ventilating of the seat as proposed herein by Applicant. Further, the wires rarely cover the entire seat, for example the side bolsters are usually non-heated. Finally, the wires in the seats may be incompatible with vehicle occupancy detectors, e.g. various air-bag and seat belt sensors.
Additionally, resistance heated type, prior art mattress pads don't offer cooling or ventilation. This is a major disadvantage in many parts of the world where the population lacks means such that air-conditioning is unavailable and a substantial portion of the year relaxing or sleeping is uncomfortable due to very warm ambient air conditions.
3. Objects of the Invention
Accordingly, it is an object of the present invention to construct a temperature-controlled cushion that is heated without the conventional resistance wires or PTC resistive elements in conductive mode within the cushion itself.
It is a further object of the present invention to construct such a cushion while minimizing the use of insulation or eliminating its use altogether.
It is a still further object of the present invention to provide such a cushion that also includes a ventilated mode.
It is a still further object of the present invention to provide such a cushion that includes convenient controls for the user.
It is a still further object of the present invention to provide such a cushion that is simple and relatively inexpensive to manufacture.
It is a still further object of the present invention to provide an accompanying power unit that is quiet and compact and located outside the cushion.
These and other objects of the present invention will become apparent upon reference to the following detailed description and accompanying drawings.